1. Field of the Invention
The present invention relates to improvements of an elliptical vibration cutting method and an elliptical vibration cutting apparatus which elliptically vibrates a cutting tool relative to a workpiece such as a steel product.
2. Description of the Prior Art
In general, a workpiece such as a steel product is cut by a conventional cutting method for providing the workpiece with a required shape.
Conventionally, a cutting tool is advanced relative to the workpiece in a constant direction, thereby cutting the workpiece by a prescribed chip removal.
Conventional cutting encounters the problem of frictional resistance or cutting resistance by the workpiece relative to the tool. This cutting resistance has a tendency to increase as the tool advances, thereby increasing the chip thickness which results in an inferior machinability.
When a ferrous material such as a steel product is cut with a diamond tool for ultraprecision working, the diamond tool is constantly in contact with the ferrous material, whereby frictional heat is generated in the contact area between the tool and the workpiece resulting in high-temperature, high-pressure working conditions. Further, carbon is dispersed in the ferrous material of the workpiece due to the chemical affinity between the diamond tool that is a form of carbon and the ferrous material. Thus, the diamond tool is subject to wear which prevents working the ferrous material with ultraprecise cutting with a diamond tool.
Elliptical vibration cutting with an elliptical vibration cutting apparatus 51 as shown in FIGS. 8, 9 and 10 is also known.
The cutting apparatus 51 performs an intermittent cutting for reducing the resistance thereby also reducing the heat conduction to the cutting tool. The intermittent cutting provides a cooling time for the cutting tool, thereby enabling an ultraprecise cutting of a ferrous material with a diamond tool.
The apparatus 51 shown in FIGS. 8 and 9 includes a cutting tool 53 cutting a workpiece 52 such as a steel product, an elliptical vibrator 54 elliptically vibrating the cutting tool 53, support members 55A and 55B supporting the elliptical vibrator 54, and a base 56 for mounting the support members 55a and 55b. The elliptical vibrator 54 includes a prismatic vibrator support body 57 forming a central portion of the elliptical vibrator 54. The body 57 has an axial projection 58 at one end and an axial projection 58A at the opposite end. Compared to the vertical dimension of the body 57, the projections 58 and 58A have reduced vertical dimensions to provide a stepped configuration. One of the projections 58 has a mounting surface 64 for mounting the cutting tool 53.
The apparatus 51 further includes piezoelectric elements 61 and 62 for generating elliptical or so-called flexible vibrations in the elliptical vibrator 54 and a control mechanism 63 individually applying prescribed sinusoidal voltages to the piezoelectric elements 61 and 62 for driving the vibrator body 57. Horizontal surfaces 59 and vertical surfaces 60 on the side surfaces of the prismatic body 57 define plane mounting surfaces for the piezoelectric elements 61 and 62.
The control mechanism 63 individually applies sinusoidal voltages of the same frequency which are 90 degrees out of phase, for example to the piezoelectric elements 61 mounted on the horizontal surfaces 59 and to the piezoelectric elements 62 mounted on the vertical surfaces 60 for energizing the piezoelectric elements, thereby generating flexible vibrations in the elliptical vibrator 54 in two perpendicular directions (vertical and horizontal directions in FIG. 9). The support members 55A and 55B form supporting points for the vibration of the body 57. The elliptical vibrator 54 is elliptically vibrated by energizing the piezoelectric elements which generate an elliptical vibration of the elliptical vibrator 54, whereby the cutting edge of the cutting tool 53 mounted on the mounting surface 64 moves along an elliptical path or xe2x80x9clocusxe2x80x9d.
Thus, the apparatus 51 can perform an elliptical vibration cutting operation on the workpiece 52 with the cutting tool 53. In other words, the apparatus 51 converts electrical energy to mechanical energy when a sinusoidal voltage is applied to the piezoelectric elements to generate a flexible elliptical vibration through the elliptical vibrator 54.
Referring to FIG. 8, there are three loops of vibration in the spacing M between the support members 55A and 55B.
When performing an elliptical vibration cutting on the aforementioned ferrous material with a diamond tool the cutting resistance and the heat conduction to the cutting tool are reduced due to the intermittent cutting operation which provides a cooling time for the cutting tool between periods when the ferrous material is engaged by the tool and ultraprecise working with the diamond tool becomes possible.
When the elliptical vibrator 54 is flexibly elliptically vibrated, however, corner portions of the prismatic body 57 remarkably impede or hinder the two-directional flexible vibration, whereby the elliptical tool path is distorted. The impeding of the vibrations results in a respective energy loss in the elliptical vibrator 54 which makes it difficult to obtain a desired locus or tool path caused by the elliptical vibration.
With the elliptical vibrator 54 having the prismatic vibrator support body 57, therefore, the elliptical vibration path of the cutting tool 53 cannot be enlarged, disadvantageously leading to an inferior machinability of the workpiece 52 cut with the cutting tool 53.
In other words, electrical energy cannot be efficiently converted to mechanical energy with the elliptical vibrator 54 having a prismatic vibrator support body 57. In FIG. 8 the body 57 has a square cross-section.
Accordingly, it is an object of the present invention in a vibration cutting apparatus having an elliptical vibrator, to enlarge a locus or path of elliptical vibration of a cutting tool that is elliptically vibrated by the elliptical vibrator to thereby improve the machinability of a workpiece cut with the cutting tool.
Another object of the present invention is to provide an elliptical vibration cutting apparatus capable of efficiently converting electrical energy to mechanical energy and to efficiently perform elliptical vibration cutting operations on a workpiece with an increased tool vibration amplitude.
Another object of the invention is to construct the vibrator, more specifically a cylindrical body portion of a tool support body forming the vibrator, in such a way that the geometric moment of inertia of the cylindrical body portion is constant or at least substantially constant for 360xc2x0 around a central longitudinal axis of the cylindrical body portion carrying at least two piezoelectric drive elements. A constant or substantially constant moment of inertia is achieved according to the invention by providing the cylindrical body portion with a circular cross-section or with a substantially cylindrical cross-section.
The term xe2x80x9csubstantially constantxe2x80x9d as used in this context to qualify the geometric moment of inertia is intended to cover any geometric moment of inertia that is distinguished from a moment of inertia of a conventional tool carrier body having an octagonal cross-section. A curve tracing the size of a conventional geometric moment of inertia of a tool carrier body with an octagonal cross-section in a polar coordinate system is also octagonal, because the moment of inertia is largest in a corner of the octagon and smallest centrally between two corners. This pattern is repeated around the octagon. Contrary thereto, the respective curve of the geometric moment of inertia of the cylindrical body portion with a substantially circular cross-section according to the invention, is also substantially circular and hence substantially constant.
The cylindrical body portion has a xe2x80x9csubstantially circular cross-sectionxe2x80x9d if it has one flattened surface area for each piezoelectric drive element and curved or arcuate surface areas circumferentially between the flattened surfaces areas. The curved or arcuate surface areas are curved or arcuate radially inwardly relative to a central longitudinal axis of the cylindrical body portion of the tool support body.
In order to solve the aforementioned technical problems, an elliptical vibration cutting method according to the present invention employs an elliptical vibrator elliptically vibrating a cutting tool for cutting a workpiece.
According to one aspect of the present cutting method, the impedance or hindrance exerted on the elliptical vibration of the elliptical vibrator by an octagonal tool support body, is reduced thereby enlarging the locus or path amplitude of the elliptical vibration of the cutting edge of the cutting tool. Preferably, the vibrator or tool support body is provided with a curved outer peripheral circumferential surface for reducing the amount of hindrance caused by a square or octagonal cross-sectional configuration. In other words, the cornered edges of the support body are removed according to the invention.
According to another aspect of the present method, the diameter of the axial projections is reduced relative to the diameter of the support body, thereby also enlarging the locus or path amplitude of the elliptical vibration on the cutting edge of the cutting tool.
According to still another aspect of the present method, the elliptical vibration is tracked and detected to provide a precise control signal which is used to control and stabilize the locus or path of the elliptical vibration applied to the cutting edge of the cutting tool.
An elliptical vibration cutting apparatus according to the present invention comprises an elliptical vibrator as a tool support body for elliptically vibrating a cutting tool for cutting a workpiece, wherein the tool support body has a cylindrical central body portion with a curved circumferential surface at least between piezoelectric elements for reducing the above mentioned hindrance of the elliptical vibration in the elliptical vibrator to thereby enlarge a locus or path of the elliptical vibration cutting edge of the cutting tool. The curved circumferential surface may be formed on at least a portion of the outer peripheral surface of a cylindrical body forming the elliptical vibrator support body. Reduced diameter projections extending coaxially to the central axis of the support body and from each end of the support body have one or more reduced diameters compared to the diameter of the central support body, whereby a stepped down support body configuration is formed. This stepped down configuration also amplifies the elliptical vibration.
The elliptical vibration cutting apparatus of the invention preferably comprises a tracking mechanism for tracking the elliptical vibration and a feedback circuit for precisely controlling the elliptical vibration in response to the tracking and in accordance with the required cutting precision.
Further, the vibration cutting apparatus according to the invention comprises supporting members supporting the elliptical vibrator support body in positions where a node of vibration is located.
Thus, electrical energy applied through a sinusoidal voltage is more efficiently converted to mechanical energy in the form of elliptical vibrations as compared to the prior art.
The amount of interference exerted on or resistance to the elliptical vibration can be reduced to readily obtain a desired locus, whereby two-directional flexible vibrations can be independently (individually) feedback-controlled when the elliptical vibrator having the cylindrical support body is elliptically vibrated.